Regardless of how a car is washed, the final rinse water normally contains minerals and impurities which leave water stains or residue marks upon evaporation. Traditionally, cars have been manually dry wiped with an absorbent cloth to avoid "spotting".
Previous automatic car wash systems have employed drying devices which attempted to eliminate or reduce the manpower needed to physically hand dry the car. Drying has most commonly been accomplished by a series of blowers which supply relatively high pressure air to blow away most of the rinse water and accelerate the evaporation of smaller droplets. These systems are inefficient because enough water is left on the car to require a worker to perform a final dry wipe with a cloth to avoid leaving water stains. In addition, the blowers consume large amounts of electrical energy.
Other prior art automatic drying devices for removing rinse water from cars include devices that sweep or draw absorbent materials across the wet surfaces. These devices are not always effective and are subject to accumulations of dirt and grime in the absorbent materials, requiring frequent removal, laundering and replacement.
In an effort to eliminate the need for hand drying or automatic drying devices, the reverse osmosis principle has been employed to purify the rinse water and remove the impurities which leave "spotting" or water stains upon evaporation. The purified reverse osmosis water dries spotless, eliminating the need for manual or automatic drying. Despite the benefits obtained by using reverse osmosis rinse water in car wash systems, the devices currently in use possess several drawbacks which reduce their effectiveness.
One drawback results from the fact that purifying water through the reverse osmosis process produces approximately one gallon of mineral-rich concentrate for each gallon of pure water produced. A typical final rinse operation requires nine to ten gallons of pure water. As a result, nine to ten gallons of mineral-rich concentrate normally become waste water which is discharged through the sewage system. Customers complain about the high levels of water consumption and the large amount of waste water which must be discharged down the sewer.
Another drawback is that when the system is not in operation for extended periods, such as overnight or during the weekends, the membrane in the reverse osmosis unit becomes contaminated with bacteria in a short period of time. This reduces the life of the membrane and results in high replacement and maintenance costs, as well as system inefficiencies.
Yet another drawback is occasioned by the fact that systems currently in use count each wash, initial rinse, and final rinse step in the operation as one cycle. Payment schedules are determined on the basis of the number of complete cycle operations. If a car is merely dusty and the operator chooses to use only the final rinse operation, the machine owner is not paid because a full cycle operation has not been used. Secondly, since the final rinse operation is used more frequently than the full cycle for which payment is received, the life expectancy of the component parts of the reverse osmosis system for full cycle operation is reduced and the system owners costs are increased. Finally, the system owners are unable to accurately monitor the number of final rinse operations which have been performed and, as a result, are unable to adhere to the desired maintenance schedule.